Foot prostheses of different types are known. The prostheses are usually designed so that an ordinary shoe can be used on the prosthesis. At a certain heel height, which can be adjusted during manufacturing of the prosthesis adapted to an individual. the prosthesis feels comfortable to walk on and to load, but without a shoe or with a different heel height the prosthesis is no longer comfortable to use since the angle of the foot with respect to the ground is no longer correct.
The most common solution to the above problem is to either angle the whole foot prosthesis downwards and forwards, or to lower the heel part when, for example, one is to walk without a shoe. Angling the prosthesis downwards does not produce an anatomically correct foot shape, i.e. one does not achieve the type of foot shape which is necessary during the use of a higher heel, and if alternatively the heel part is lowered, this instead results in a lengthening of the leg which will cause discomfort, especially in the back.
WO93/24080 (same applicant) describes the general design of a foot prosthesis with a support part and a foot means which cooperates with the support part, wherein the foot means comprises a forefoot part arranged so that it is slidably fixed to the support part in its axial direction and separately a heel part intended to be arranged at the lower end of the support part.
SE-B-8504225-5 a foot prosthesis is described having a central part which supports the sole, heel and leg parts. In this prosthesis the heel is movably arranged in relation to the central part of the prosthesis and to the part of the sole of the foot which is fixedly joined with the central part. Movement of the heel is obtained by the latter being connected with the rear part of the central part by means of a bar which can be locked in a hole in said part and which in the unlocked position is displaceable in relation to the central part for adjusting the heel in relation to the foot sole. In this device a lengthening of the leg is obtained by the hole being moved downwards in relation to a reference point, e.g. the knee of the user.
U.S. Pat. No. 4,547,913 describes a completely different solution to the problem. Here the prosthesis is made of three rigidly connected parts, the leg part, the foot part and the heel part made of fibre reinforced resin, where the material and design of the parts gives flexibility to the prosthesis.
In U.S. Pat. No. 5,181,933 is described a prosthesis foot comprising essentially two curvilinear parts of which one extends from the attachment part to the toe part of the foot. Halfway at between the two ends and underneath the first curvilinear part a second curvilinear part is attached in such a way as to provide the heel part of the foot prostheses.
In FR C 907 306 a prosthesis foot is described, in which the foot-part and the toes are separated by an opening. The parts are connected through a number of steel bands. The foot and the toe part are also connected through a damper comprising a cylinder and a piston and the damper connected to the foot and the toe part respectively.
In DE C 841 192 another foot prostheses is described which comprises a foot prostheses having a toe part which may be bent. The two parts are connected through a bendable sole and are also connected via a flexible elongated rubber piece extending into two holes in the two parts respectively.
These three prostheses comprise a prostheses foot which is complete in the sense of the forefoot and the heel being directly connected to each other.
U.S. Pat. No. 5,181,933 is described a prosthesis foot comprising essentially two curvilinear parts of which one extends from the attachment part to the toe part of the foot. Halfway between the two ends and underneath the first curvilinear part a second curvilinear part is attached in such a way as to provide the heal part of the foot prostheses.
In FR,C,907 306 a prosthesis foot is described, in which the foot-part and the toes are separated by a opening. The parts are connected through a number of steel bands. The foot and the toe part are also connected through a damper comprising a cylinder and a piston and the damper connected to the foot and the toe part respectively.
In DE,C,8411.92 another foot prostheses is described which comprises a foot prostheses having a toe part which may be bent. The two parts are connected through a bendable sole and is also connected via a flexible elongated rubber piece extending into two holes in the two parts respectively.
These three prostheses comprise a prostheses foot which is complete in the sense of the fore foot and the heal being directly connected to each other.
During the production of foot and leg prostheses a number of factors have to be taken into account. The normal foot can move in all planes, individually or in combination. The lower leg of a person consists of two bones which by cooperation with each other and with the ankle joint permit a rotational movement, torsion of the lower leg, which continues in a rotation of the foot. Furthermore, the calf muscles of the lower leg provide a variable pushing off force, i.e. adapted for the specific purpose,
There are today technical solutions for solving this problem to some extent, e.g. in SE-B-8201389-7, where the foot prosthesis consists of a continuous hollow core, which is secured directly onto the leg prosthesis adapter and which by virtue of its design, with rigid and elastic region provides mobility in the dorsal plantar direction. The foot however, does not have any capacity for energy storage, it has no adjustable heel and it is not made from a light but strong composite mateial.
Moreover, in the natural foot an adjuscent of the attitude of the heel takes place when the height of the heel increases. This can be illustrated most clearly through observing the movement which takes place when the foot is being introduced into a shoe or when walking on tiptoe. What happens is that the muscles on the back of the lower leg contract and in this way the heel is lifted, while at the same time as the heel is lifted an angling of the forefoot takes place in the case of a normal walking movement. The higher the heel is lifted, the greater is the angle obtained between the forefoot and the adjoining part of the foot.